The flight control system of an aircraft connects the piloting members (control column, rudder bar, etc.) and the aerodynamic tip-control surfaces. Modern jetliners have electric flight control systems in which the mechanical actions on the piloting members are converted into analog signals that are sent to actuators maneuvering the control surfaces.
FIG. 1 illustrates a centralized flight control system 100, known from the state of the art. We have shown a piloting member 110, for example a side-stick controller, equipped with one or more sensors 115, for example position sensors and/or angular sensors providing position and/or orientation information to the flight control computer 120. The computer 120 determines, from information received from the various piloting members 110, including the auto-pilot (not shown) and/or, if applicable, airplane sensors 150 (accelerometer, rate gyro, inertial unit), the flight controls to be applied to the actuators 130. These actuators are typically hydraulic cylinders controlled by solenoid valves or electric motors acting on the aerodynamic flight-control surfaces of the aircraft 140. The actuators 130 on the one hand, and the aerodynamic flight-control surfaces 140 on the other hand, are equipped with sensors respectively denoted 135 and 145. These sensors inform the computer 120 on the positions and/or orientations of the mobile elements of the actuators as well as those of the control surfaces. For example, one sensor 135 could indicate the translational position of a cylinder, one sensor 145 the orientation of a flap.
The computer 120 has both a command function and a monitoring function. It is connected to the actuators by first cables 133 intended to transmit the analog control signals. It is also connected to the sensors 135 and 145 respectively equipping the actuators and the control surfaces themselves by second cables 137 and third cables 147. It can thus, at any time, monitor the status of the actuators and verify that the commands have been carried out correctly.
In reality, a flight control system is made up of several independent elementary systems, each having its own computers, its own set of sensors and actuators, and its own network of cables.
This flight control system has a certain number of drawbacks, including the need to deploy a large number of cables between the computers on the one hand and the actuators and control surfaces they control on the other. This cable deployment strains the aircraft's weight budget and increases the exposure to risks of electromagnetic disturbances.
In order to resolve these drawbacks, it was proposed in French application no. 08 50806, filed in the Applicant's name and not published, to use a distributed flight control system (DFCS) organized around a multiplexed communication bus. In this DFCS, certain control and monitoring functions are taken off-board the central computers towards remote terminals situated at actuators. The command and monitoring messages between the central computers and remote terminals are sent on said multiplexed bus.
Furthermore, in order to guarantee a high level of safety, each elementary system of the flight control system is powered by a separate energy source.
FIG. 2 illustrates the overall structure of a flight control system of an Airbus A380. The flight control system comprises four independent elementary systems respectively designated SYST1, SYST2, SYST3 and BCM. System SYST1 comprises a primary computer denoted PRIM1 and a second computer denoted SEC1. Likewise, systems SYST2 and SYST3 each comprise a primary computer (PRIM2, PRIM3) and a secondary computer (SEC2, SEC3). The control system BCM is a back-up system.
The computers PRIM1, PRIM2, PRIM3, SEC1, SEC2, SEC3 and BCM are specific computers for the computations of the flight controls. The primary computers PRIM1, PRIM2 and PRIM3 all have the same structure. On the other hand, the secondary computers SEC1, SEC2 and SEC3 have a structure distinct from that of the primary computers.
The flight control system can operate in several modes. The primary computers allow the flight control system to operate in nominal mode 210, i.e. to control all of the control surfaces of the aircraft. The secondary computers operate in standby mode or slave mode of a master primary computer. By default, the master computer is the primary computer PRIM1. It sends the flight commands to all of the other primary computers as well as to the secondary computers.
In the event of failure of computer PRIM1, computer PRIM2 takes over, and if the latter is defective, PRIM3 takes over in turn. When all of the primary computers are defective, the secondary computers take over in the same order SEC1, SEC2, SEC3. In mode 220, the secondary computers implement laws of deteriorated operation, i.e. more robust than those used by the primary systems. Moreover, the secondary computers do not make it possible to perform the auto-pilot function of the airplane, unlike the primary systems. Lastly, the secondary computers control some of the control surfaces of the aircraft from instructions from computer PRIM1 or, failing that, from those of another primary computer, if the latter is defective.
The BCM (Back-up Control Module) computer corresponds to a basic operation 230.
Systems SYST1 and SYST3 are powered by a first electrical energy source, E1, for example a variable frequency voltage generator (VFG). System SYST2 is powered by a second electrical energy source E2, which is independent of the first but of the same type. Lastly, control system BCM is powered by a back-up power supply (BPS), formed by a generator mounted on a hydraulic circuit whereof the fluid is driven by pumps which themselves are mechanically driven by the reactors.
A first object of the present invention is to propose a distributed flight control system having an integrated modular architecture simpler than that of the prior art while guaranteeing a high level of safety. A second object of the present invention is to reduce the number of computers in the flight control system without sacrificing the requisite level of safety.